What is a RIP – Raster Image Processor?

What is a RIP – Raster Image Processor?

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What is a RIP – Raster Image Processor?
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What is a RIP? A simple analogy is Photoshop. Have you ever opened a PDF with Photoshop? The ‘Import PDF’ dialogue window prompts you with two important fields: resolution and mode. After inputting resolution, mode and clicking OK, Photoshop starts the raster image process – converting the PDF into a bitmap. Raster is another term for bitmap.

 

Our friend ‘amoeba’ shown at varying bitmap resolutions. Notice the outline super-imposed at various resolutions. Higher bitmap resolutions create longer processing times in the RIP (raster image processor).

 

This is essentially what happens in prepress, however with much more sophisticated software and hardware. The main difference between the two is bit depth. Photoshop will convert a PDF file into an 8-bits/channel bitmap, while a high-end prepress RIP will convert the PDF file into a 1-bit/channel bitmap. 1 bit/channel is binary – on or off, black or white. 8-bits/channel is grayscale, meaning 28 =256 levels of gray – continuous tone.

In Photoshop, a common resolution would be 300 pixels per inch. In prepress, resolutions can go as high as 5080 dots per inch rendering a printing plate. Note the difference between pixels and dots. Images are composed and displayed as pixels, while dots are what are used to render a printing plate.

In essence, the RIP is the device that converts type, vector graphics, continuous tone images, screens and all other content into a high resolution grid of binary pixels that the laser will render onto a printing plate. Imagine a 5080 dots per inch grid at a size of 40″x30″ with various pixels turned on or off. This is a printing plate. Since a printing press cannot print continuous tone, these tiny little dots create the illusion of continuous tone. Stochastic printing-FM screening is responsible for creating the illusion of the 8-bit grayscale with only 1-bit binary imaging. Color Images are separated into CMYK and screened with stochastic-FM dots.

Stochastic printing is far superior than conventional printing halftone dots because of their ability to render incredible detail.

Raster Image Processors are now running Adobe PDF Print Engine 2 software replacing Postscript. That’s why PDFs are the standard for submitting files for press.

 

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    2 Comments

  1. Thanks – this is very interesting, I was looking for a way to explain this to my sales people – who are always asking why ripping takes so long. Great article

  2. Dear sir,

    I do pantone color and spot color with software recipe for offset at Chennai south india and your website is very informative and its worlds best but in india printers use iso coated v2.

    regards
    sowri

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